The present invention relates to an assembly of a hub and hub-holder for vehicles equipped with a central tire inflation system and, more particularly, sealing means or rotating joints between the hubs and hub holders of these vehicles.
In order to be able to use tire inflation installation arranged on board a vehicle during the travel of the vehicle, it is necessary to provide each wheel with an air-tight rotating joint in order to assure a connection between an air compressor on the vehicle and each of the tires through the hub of each wheel.
Such rotating joints are described, for instance, in U.S. Pat. No. 4,730,656. In that patent, a flexible sealing lip 72 is clamped permanently against its cylindrical sealing surface 68 by a "circular spring 78 which exerts a radial force towards the inside". Accordingly, in this known system, the flexible parts which assure the tightness are always in rotating contact. This arrangement has several drawbacks: a certain amount of power is absorbed uselessly, which causes a harmful liberation of heat; furthermore, the parts in rotating contact wear out rapidly, which impairs their reliability and makes their replacement necessary. U.S. Pat. No. 4,804,027 proposes a device for solving this problem. In this second patent, a toroidal lobe 50 of rubber which is fastened to the stationary hub rests against a cylindrical sealing surface 22 of the movable hub; when the air pressure is high (during inflation), the lobe rests firmly against said sealing surface so as to assure tightness; upon return to atmospheric pressure "the lobes 50 rest against the surfaces 22 with a very slight pressure, or even without any contact pressure at all". This arrangement makes it possible significantly to reduce the contact pressures between the sealing lips and the corresponding sealing surfaces during periods of non-use of the inflation means. However, this arrangement does not permit the use of rigid materials in order to assure the tightness. In fact, the tightness is assured by the radial deformation of a resilient lobe. Accordingly, this lobe and the associated device always present problems of wear and therefore of life.
In the following, the term "hub" will be used to cover all the parts movable in rotation around the fixed hub carrier of a vehicle axle with the exception of the tires and the connecting ball bearings. Thus the term "hub" will include the hub proper, but also the wheel which is rigidly fastened to the hub.
Similarly, "hub holder" will be used to designate all the stationary parts of the axle.